1. Field of the Invention
The present invention is in the field of mechanical locking devices and specifically relates to a device of the type in which the locking is effected by a coiled spring which grips a rod, for clamping the rod against translational motion relative to a housing and for selectively enabling such motion.
2. The Prior Art
Friction brake locking devices are known in which a rod extends into a cylindrical housing. Normally, the rod is locked with respect to the housing so that axial translational motion of the rod relative to the housing is prevented. However, the device can be selectively actuated to an unlocked state in which such motion is enabled. A coiled spring is affixed to the housing and is coaxial with the rod in the locked state. The spring grips the curved surface of the rod to prevent the rod from moving with respect to the housing. An actuation lever permits an operator to partially unwind the spring, thereby increasing its inside diameter so that the spring no longer grips the rod, which may then be moved freely axially within the coiled spring.
The use of a coiled spring to grip a rod extending coaxially through the spring is well known. A number of locking devices making use of this basic principle are known in the art.
Among the prior art devices is the locking device of U.S. Pat. No. 3,249,180 issued May 3, 1966 to Torossian. As shown in FIG. 10 of the Torossian patent, the spring is affixed at one end to a fixed ring 109, while the other end of the spring 108 is engaged by a rotatable ring 110. The ring 110 engages a longitudinally-extending groove in the rod, so that when the rod is rotated, the ring also rotates to tighten the grip of the spring on the rod.
The device of the Torossian patent includes an abutment on the rotating ring and on the fixed ring to cause the spring to become cocked on the rod, in which state the gripping force of the spring on the rod increases with the axial load, thereby resulting in a true locking action. This aspect of the mechanics of the device was also recognized by Howell in U.S. Pat. No. 2,750,996 issued June 10, 1956. However, as shown most clearly in FIG. 5 of the Howell patent, in his device only the fixed sleeve 25 is provided with a beveled base 40, and the device is actuated by rotating the opposite end 31 of the spring. Accordingly, in Howell's device it is necessary to unwind the many turns of the spring to transmit the enlargement of the diameter to the fixed end of the spring. This necessitates an unnecessarily long stroke for the actuating lever.
Another type of prior art device is that shown in U.S. Pat. No. 3,874,480 issued Apr. 1, 1975 to Porter et al. As can best be seen in FIG. 2 of the Porter et al. patent, two springs are disposed coaxially to extend in opposite directions from a central actuating lever to fixed locking bushings located at opposite ends of a housing sleeve. One of the locking bushings locks the device in tension and the other locks it in compression. The interaction of the last two or three coils at the ends of the springs distal to the actuating lever with the locking bushings is responsible for the locking effect.
It is noteworthy that while only one of the springs in the Porter et al. device is effective at a particular instant to oppose tension or compression, unlocking of the device nonetheless requires unwinding both springs simultaneously by use of the actuating lever. The lever must be moved through a sufficient stroke that the entire length of each spring is unwound, to ensure that the last two or three turns will be unwound. This necessitates a large actuating lever stroke which is opposed by the combined forces of both springs resisting unwinding. Consequently, in contrast to the present invention, both the actuating lever stroke and the force needed for its operation are relatively large. While such structure functions well, there are installations where, due to space limitations and the like, there is a need for a friction brake type of device in which the stroke of the actuating lever is comparatively small and which operates at a comparatively smaller force.
The structure of the Porter et al. device, while satisfactory in performance, is somewhat complicated because of the assembly of the device. The end bushings which affixed the distal ends of the springs to the housing sleeve had to be rotated during the assembly process to positions in which the proximal ends of both of the springs abutted the actuating lever in a balanced manner. Such rotation necessitated that the grip of at least one of the springs be released by unwinding that spring. In practice, assembly required a highly-skilled wind-up operation to assure that both springs were properly compacted and twisted against the actuating lever. In contrast, in the present invention this complicated assembly procedure is not required.
The following patents can be distinguished from the present invention on the basis that they do not include an abutment or beveled bushing against which the spring bears, and accordingly the true locking action discussed above is not employed. These patents include U.S. Pat. No. 2,434,480 to Anderson issued Jan. 12, 1948; U.S. Pat. No. 3,320,595 to Kedem; U.S. Pat. No. 2,429,383 to Arens, and U.S. Pat. No. 3,064,766 to Hanizeski.
There are instances in which it is desirable to have a mechanical locking device in which the force needed to release the lock mechanism is reduced while also reducing the amount of movement of the actuating lever to effect release. A typical such application is in the automotive seat field in which movement of the seat back between an upright and reclining position should be accomplished smoothly and without a snap type action. Further, where the locking mechanism is of the direct control actuation type, i.e., the user manipulates a release lever, in contrast to some type of linkage mechanism of the remote control type, large forces for release or large movements of the actuating lever should be avoided.
While the above may be accomplished, one of the practical considerations is to accomplish these objectives with a relatively inexpensive device, but one which is capable of functioning properly over an extended period of time. Further, the device should be essentially maintenance free and capable of functioning over extreme temperature ranges and not adversely affected by water, dirt, dust and the like.